Investigation of ferroelectric nanopowders by EPR method

Abstract

BaTiO 3 nanopowders with different particle sizes have been studied by Electron Paramagnetic Resonance method over a temperature range covering the ferroelectric-paraelectric transition. Iron and manganese impurities were used as probes for these experiments. The evolution of the spectra over the transition was observed through 1) the change in symmetry of Fe 3+ from tetragonal to cubic and 2) the appearance beyond T C of Mn 2+ characteristic lines. The results were analyzed according to a theoretical model proposed by one of the authors to extract the distribution of the particles size from the electron paramagnetic resonance spectra. Both the mean particle radius R 0 and the dispersion σ showed a very good agreement with the data obtained from direct measurement of the size distribution. This evidences both the critical influence of the nanoparticles sizes distribution on the EPR spectra's main features and on the temperature dependence of the polarization. In the framework of the theoretical model proposed by one of the authors the distribution of the particles size was extracted from the electron paramagnetic resonance spectra.1 Introduction The decrease of devices' dimensions in microelectronic requires a deep understanding of the influence of the size on the material properties; in the last decade, scientists and engineers have in particular shown a growing interest in size effects in ferroelectric (FE) materials [1][2][3][4][5]. Many properties like the Curie temperature, the electrical polarization, the coercive field, the switching time, etc were shown to be dependent on the size of particles. Size-driven FE-paraelectric (PE) phase transition was shown to be the most prominent size effect in FE nanomaterials. The existence of a critical size (the size at which the ferroelectricity FE disappears) in FE nanoparticles at room temperature (RT) was also revealed using various experimental methods. However, there is a broad scattering of this last property values depending on the method used [6][7][8]; it follows that the development of an accurate method to determine the critical size still remains a challenge.It is known that materials properties are inhomogeneously distributed inside a nanoparticle samples and that the influence of such inhomogeneity increases as the size of the particle decreases. The local properties therefore becomes of primary importance to exactly determine the effect of a size distribution and fully understand the volume smoothed properties. For this purpose, the application of radiospectroscopic methods (nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR)) were shown to be particularly useful [8,9]. In Ref.[8] however average value of polarization instead of local one was used in the consideration, which gave only rough estimation for the obtained quantities. In our previous paper [9] we used the local polarization and its dependence on the particle size as well as particle size distribution. This allows to obtain more accurate value of the critical radius and ...

Low temperature dielectric relaxation and charged defects in ferroelectric thin films

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Surface-induced piezomagnetic, piezoelectric, and linear magnetoelectric effects in nanosystems

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“…Results for , and are presented in the Table 1. It is seen from the Table 1 that a nonpiezoelectric and nonpiezomagnetic bulk material with m3m, m′3m′, m′3m and m3m′ symmetry becomes piezoelectric and piezomagnetic in the vicinity of surface with different tensors, which depend on the surface symmetry group, the influence of surface on the symmetry and properties being essential on the distances of several tens nm from the surface [26,27,28].…”

Specific core-shell approaches and related properties in nanostructured ferroelectric ceramics

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